Cels had early shown a methodical temperament and a pronounced taste for botany. He studied under Bernard de Jussieu and Louis-Guillaume Le Monnier, and he was sympathetic to the ideas of Rousseau.
Cels entered the office of the Ferme Générale in Paris in 1759. In 1761 he became a collector of revenues at the Little Saint Bernard Pass and a short while later that of the octroi at Saint-Jacques gateway. With the latter position came the use of a house with about three-quarters of an acre of land, on which he laid out a rich botanical garden.
The Revolution abolished his office in 1790, forcing Cels to find a new way of making a living. He retired to Montrouge and devoted himself to the cultivation and sale of plants. He encountered serious difficulties, however. Made responsible by the Convention for a considerable sum stolen from his strongbox in 1789, upon the looting of the octroi barrière, he had to sell his large library in order to acquit himself; moreover, on several occasions he had to transfer his cultivation to other locations.
At the beginning of the nineteenth-century Cels' holdings were in the plain near Montrouge, about one kilometer from Paris, near “the Jansenist windmill”; they finally totaled about eighteen acres, covered by greenhouses, beds, borders, and especially by a tree nursery and small ornamental and fruit trees. In Cels' garden, which became one of the most beautiful in Europe, were drawn and described several of the species published in the Stirpes novae (1784-1791) of Charles-Louis L’Héritier, in the Histoire naturelle des plantes grasses (1799) and the Astra-gologia (1802) of Augustin-Pyramus de Candolle, and in the Liliacées (1802-1816) of P. J. Redouté. Cels applied himself particularly to propagating the rare plants introduced into France by the naturalist voyagers of his time (several of whom were his personal friends): Joseph Dombey, André Michaux, Louis Bose, Guillaume-Antoine Olivier, Jean Bruguières, Pierre Auguste Broussonet, Jacques de La Billardière, Hippolyte Nectoux, and Anselme Riedlé. He carried on an important correspondence with the principal botanists of Europe, who provided him with new species, and he generously placed his abundant plant collection at their disposal. He also sent plants to the botanical garden at Kew. A member of the Commission of Agriculture and then of the Council of Agriculture, Cels prevented the destruction of parks and châteaus during the Revolution; he also contributed to the formation and the direction of the agricultural institutions at Le Rainey, Sceaux, and Versailles. The majority of his writings appeared anonymously.
Cels' son, François, was his collaborator and continued his father's work.